Mass accumulation rates, age, sedimentation rate and bulk density at the East Pacific Rise

The rate at which hydrothermal precipitates accumulate, as measured by the accumulation rate of manganese, can be used to identify periods of anomalous hydrothermal activity in the past. From a preliminary study of Sites 597 and 598, four periods prior to 6 Ma of anomalously high hydrothermal activity have been identified: 8.5 to 10.5 Ma, 12 to 16 Ma, 17 to 18 Ma, and 23-to-27 Ma. The 18-Ma anomaly is the largest and is associated with the jump in spreading from the fossil Mendoza Ridge to the East Pacific Rise, whereas the 23-to-27-Ma anomaly is correlated with the birth of the Galapagos Spreading Center and resultant ridge reorganization. The 12-to-16-Ma and 8.5-to-10.5-Ma anomalies are correlated with periods of anomalously high volcanism around the rim of the Pacific Basin and may be related to other periods of ridge reorganization along the East Pacific Rise. There is no apparent correlation between periods of fast spreading at 19°S and periods of high hydrothermal activity. We thus suggest that periods when hydrothermal activity and crustal alteration at mid-ocean ridges are the most pronounced may be periods of large-scale ridge reorganization.

CaCO3, foraminifer fragmentation, benthic carbon isotopes, coarse lithic counts and radiogenic isotopes (Sr, Nd, Pb) of the Pliocene and earliest Pleistocene terrigenous component (3.3-2.4 Ma) of IODP Site 306-U1313

We present Plio-Pleistocene records of sediment color, %CaCO3, foraminifer fragmentation, benthic carbon isotopes (d13C) and radiogenic isotopes (Sr, Nd, Pb) of the terrigenous component from IODP Site U1313, a reoccupation of benchmark subtropical North Atlantic Ocean DSDP Site 607. We show that (inter)glacial cycles in sediment color and %CaCO3 pre-date major northern hemisphere glaciation and are unambiguously and consistently correlated to benthic oxygen isotopes back to 3.3 million years ago (Ma) and intermittently so probably back to the Miocene/Pliocene boundary. We show these lithological cycles to be driven by enhanced glacial fluxes of terrigenous material (eolian dust), not carbonate dissolution (the classic interpretation). Our radiogenic isotope data indicate a North American source for this dust (~3.3-2.4 Ma) in keeping with the interpreted source of terrestrial plant wax-derived biomarkers deposited at Site U1313. Yet our data indicate a mid latitude provenance regardless of (inter)glacial state, a finding that is inconsistent with the biomarker-inferred importance of glaciogenic mechanisms of dust production and transport. Moreover, we find that the relation between the biomarker and lithogenic components of dust accumulation is distinctly non-linear. Both records show a jump in glacial rates of accumulation from Marine Isotope Stage, MIS, G6 (2.72 Ma) onwards but the amplitude of this signal is about 3-8 times greater for biomarkers than for dust and particularly extreme during MIS 100 (2.52 Ma). We conclude that North America shifted abruptly to a distinctly more arid glacial regime from MIS G6, but major shifts in glacial North American vegetation biomes and regional wind fields (exacerbated by the growth of a large Laurentide Ice Sheet during MIS 100) likely explain amplification of this signal in the biomarker records. Our findings are consistent with wetter-than-modern reconstructions of North American continental climate under the warm high CO2 conditions of the Early Pliocene but contrast with most model predictions for the response of the hydrological cycle to anthropogenic warming over the coming 50 years (poleward expansion of the subtropical dry zones).

Geochemistry of lavas from the Lau-Tonga arc and back-arc system

Detailed comparison of mineralogy, and major and trace geochemistry are presented for the modern Lau Basin spreading centers, the Sites 834-839 lavas, the modern Tonga-Kermadec arc volcanics, the northern Tongan boninites, and the Lau Ridge volcanics. The data clearly confirm the variations from near normal mid-ocean-ridge basalt (N-MORB) chemistries (e.g., Site 834, Central Lau Spreading Center) to strongly arc-like (e.g., Site 839, Valu Fa), the latter closely comparable to the modern arc volcanoes. Sites 835 and 836 and the East Lau Spreading Center represent transitional chemistries. Bulk compositions range from andesitic to basaltic, but lavas from Sites 834 and 836 and the Central Lau Spreading Center extend toward more silica-undersaturated compositions. The Valu Fa and modern Tonga-Kermadec arc lavas, in contrast, are dominated by basaltic andesites. The phenocryst and groundmass mineralogies show the strong arc-like affinities of the Site 839 lavas, which are also characterized by the existence of very magnesian olivines (up to Fo90-92) and Cr-rich spinels in Units 3 and 6, and highly anorthitic plagioclases in Units 2 and 9. The regional patterns of mineralogical and geochemical variations are interpreted in terms of two competing processes affecting the inferred magma sources: (1) mantle depletion processes, caused by previous melt extractions linked to backarc magmatism, and (2) enrichment in large-ion-lithophile elements, caused by a subduction contribution. A general trend of increasing depletion is inferred both eastward across the Lau Basin toward the modern arc, and northward along the Tongan (and Kermadec) Arc. Numerical modeling suggests that multistage magma extraction can explain the low abundances (relative to N-MORB) of elements such as Nb, Ta, and Ti, known to be characteristic of island arc magmas. It is further suggested that a subduction jump following prolonged slab rollback could account for the initiation of the Lau Basin opening, plausibly allowing a later influx of new mantle, as required by the recognition of a two-stage opening of the Lau Basin.

Geochemistry of basalts from ODP Hole 113-690C

Basalts from Maud Rise, Weddell Sea, are vesicular and olivine-phyric. Major, trace, and rare earth element concentrations are similar to those of alkali basalts from ocean islands and seamounts. The rocks are low in MgO, Cr, Ni, and Sc, and high in TiO2, K2O, P2O5, Zr, and LREE contents. The abundance of "primary" biotite and apatite in the matrix indicates the melting of a hydrous mantle. Prevalence of olivine and absence of plagioclase in the rocks suggests that the volatile in the melt was an H2O-CO2 mixture, where H2O was <0.5. Mantle derived xenocrysts in the basalt include corroded orthopyroxene, chromite, apatite, and olivine. Olivine (Fo90) is too magnesian to be in equilibrium with the basalts, as they contain only 5-6 wt% MgO. Based on the presence of mantle xenocrysts, the high concentration of incompatible elements, the spatial and chemical affinity with other ocean island basalts from the area, and the relative age of the basalt (overlain by late Campanian sediments), it is suggested that Maud Rise was probably generated by hot-spot activity, possible during a ridge crest jump prior to 84 Ma (anomaly 34 time). Iddingsite, a complex intergrowth of montmorillonite and goethite, is the major alteration product of second generation olivine. It is suggested that iddingsite crystallized at low temperatures (<200°C) from an oxidized fluid during deuteric alteration. Vesicles are commonly filled by zeolites which have been replaced by K-feldspars.

Proglacial river dataset from the Akuliarusiarsuup Kuua River northern tributary, Southwest Greenland, 2008 - 2013, version 2.0

The dataset contains measurements of river stage and discharge for one sites along the Akuliarusiarsuup Kuua River's northern tributary, with 30 minute temporal resolution between June 2008 and August 2013 This river is a tributary to the Watson River discharging into Kangerlussuaq Fjord by the town of Kangerlussuaq, Southwest Greenland. Additional data of water temperature, air pressure are also provided. Compared to version 1.0 of the dataset, this dataset used a total of 36 in situ discharge observations collected between 2008 and 2012 to construct the rating curve. Furthermore, data of Station AK-004-001 between 2010-09-06T11:30 to 2010-09-07T13:30 have been removed from version 2.0 because these values were likely caused by backflow when a jokulhlaup from a large glacier dammed lake caused increased water levels in the downstreams lake. Thus, data measured at AK-004-001 between 2010-09-06T11:30 to 2010-09-07T13:30 are not representative for the AK-004 catchment.

Downhole variations in grain sizes at DSDP/ODP Hole 504B

The maximum grain sizes of plagioclase and magnetite in the groundmass of the sheeted dike complex drilled at Hole 504B have been measured. Downhole variations through a 440-m-long section show a crude zig-zag pattern consisting of a gradual decrease or increase followed by an abrupt jump. The gradual decrease or increase in grain size extends over many lithologic units, and hence, does not reflect variations in grain size within a single dike. Such a zig-zag pattern is well explained by grain-size variations through multiple dikes. By using the observed inclination of sheeted dikes of 81° ± 2.5°, thickness of the multiple dikes varies from 0.7 to 8.5 m and averages to 4 ± 1 m. The average thickness of individual dikes forming multiple dikes is 0.8 m. We expect such multiple dikes to be formed during rifting events beneath mid-oceanic spreading ridges. If the average expansion at rifting episodes is twice as wide as the average width of the multiple dike units, the full spreading rate of 7.2 cm/yr of Cocos Ridge gives 112 ± 33 yr for a time interval of the rifting. A simple one-dimensional conductive cooling model is applied to solidification of multiple dikes. Numerical simulations show that the grain-size variations observed through the drill hole are more consistent with a model where a new injection of a dike occurs periodically with a constant time interval rather than one where the next dike intrudes just after the solidification of the previous one. Grain-size variations within simple dikes from Iritono, Japan, and those for Makaopuhi lava lake, Hawaii, show that square root of crystallization time is linearly correlated with the logarithm of plagioclase size. By using an empirically derived relationship between these two variables, the variations of plagioclase size through Hole 504B are directly compared with the calculated times for crystallization. Each rifting episode at the Costa Rica Rift lasts for several years, and periodic injection of a new dike occurs into the center of a previously solidified multiple dike at time intervals varying from 1 to 12 months.

Composition of rocks and minerals from the Bolshoy Lyakhovsky Island (New Siberian Islands)

In the southeast of the Bolshoi Lyakhovsky Island there are outcrops of tectonic outliers composed of low-K medium-Ti tholeiitic basic rocks represented by low altered pillow basalts, as well as by their metamorphosed analogs: amphibolites and blueschists. The rocks are depleted in light rare-earth elements and were melted out of a depleted mantle source enriched in Th, Nb, and Zr also contributed to the rock formation. The magma sources were not affected by subduction-related fluids or melts. The rocks were part of the Jurassic South Anyui ocean basin crust. The blueschists are the crust of the same basin submerged beneath the more southern Anyui-Svyatoi Nos arc to depth of 30-40 km. Pressure and temperature of metamorphism suggest a setting of "warm" subduction. Mineral assemblages of the blueschists record time of a collision of the Anyui-Svyatoi Nos island arc and the New Siberian continental block expressed as a counter-clockwise PT trend. The pressure jump during the collision corresponds to heaping of tectonic covers above the zone of convergence 12 km in total thickness. Ocean rocks were thrust upon the margin of the New Siberian continental block in late Late Jurassic - early Early Cretaceous and mark the NW continuation of the South Anyui suture, one of the main tectonic sutures of the Northeastern Asia.

Sea surface temperature reconstruction for sediment core KNO5103-0029GGC

We present a 15 kyr sea surface temperature (SST) record for a high sedimentation rate core (KNR51-29GGC) from the Feni Drift off of Ireland, based on an organic geochemical technique for paleotemperature estimation, U37 K'. We compare the U37 K' temperature record to planktonic foraminiferal delta18O and foraminiferal assemblage SST estimates from the same sample horizons. U37 K' gives SST estimates of 13°C for the early deglacial and 18°C for the Holocene and Recent, whereas assemblages give estimates of 9°C and 13°C, respectively. As in nearby core V23-81, we find Ash Zone 1, the Younger Dryas increase in Neogloboquadrina pachyderma sinistral abundance, and maximum abundance of this species during glaciation. N. pachyderma dextral oxygen isotopic analyses have a late glacial to interglacial range of 1.5 per mil. A reduction of about 1 per mil in delta18O occurred at about 12 ka, whereas U37 K' and the foraminiferal fauna indicate a 2°C warming. This implies a 0.9 per mil salinity effect on delta18O which we attribute to meltwater freshening. All three parameters indicate cooling during the Younger Dryas. U37 K' SST estimates show that the major shift from deglacial to interglacial temperatures occurred after the Younger Dryas in termination 1b, in contrast to the assemblage data, which show this jump in SST at the end of the glaciation during termination Ia. Differences between the two SST estimators, which may result from their different (floral versus faunal) sources, are more pronounced between transitions Ia and Ib. This may reflect different habitats under the unusual sea surface conditions of the deglaciation.

Multi-temporal shoreline change rates on Taku Atoll

Recent-past shoreline changes on reef islands are now subject to intensified monitoring via remote sensing data. Based on these data, rates of shoreline change calculated from long-term measurements (decadal) are often markedly lower than recent short-term rates (over a number of years). This observation has raised speculations about the growing influence of sea-level rise on reef island stability. This observation, however, can also be explained if we consider two basic principles of geomorphology and sedimentology. For Takú Atoll, Papua New Guinea, we show that natural shoreline fluctuations of dynamic reef islands have a crucial influence on the calculation of short-term rates of change. We analyze an extensive dataset of multitemporal shoreline change rates from 1943 to 2012 and find that differing rates between long- and short-term measurements consistently reflect the length of the observation interval. This relationship appears independent from the study era and indicates that reef islands were equally dynamic during the early periods of analysis, i.e. before the recent acceleration of sea-level rise. Consequently, we suggest that high rates of shoreline change calculated from recent short-term observations may simply result from a change in temporal scale and a shift from geomorphic equilibrium achieved over cyclic time towards an apparent disequilibrium during shorter periods of graded time. This new interpretation of short- and long-term shoreline change rates has important implications for the ongoing discussion about reef island vulnerability, showing that an observed jump from low to high rates of change may be independent from external influences, including but not limited to sea-level rise.

Composition and crystal parameters of carbonate-apatites from animal teeth and bones and from phosphate rocks of the ocean bottom

Samples of recent to Miocene fish and marine mammal bones from the bottom of the Atlantic and Pacific Oceans and Miocene Maikop deposits (Transcaspian region) are studied by X-ray diffraction technique combined with chemical and energy-dispersive analyses. Changes of lattice parameters and chemical composition of bioapatite during fossilization and diagenesis suggest that development of skeletal apatite proceeds from dahllite-type hydroxyapatite to francolite-type carbonate-fluorapatite. It is assumed that jump-type transition from dahllite to francolite during initial fossilization reflects replacement of biogeochemical reactions in living organisms, which are subject to nonlinear laws of nonequilibrium thermodynamics, by physicochemical processes according to the linear equilibrium thermodynamics.